Signal system



Sept. 22, 1942- a. J. KlNssuR SIGNAL SYSTEM Filed Oct. 19, 1940 nvVENTOR By B. J. K/NSBURG A T'mpuE- Patented Sept. 22, 1942 e I, r

SIGNAL SYSTEM Boris J. Kinsburg, Riverdale, N. Y., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application October 19, 1940, Serial No. 361,879

Claims.

This invention relates to signal systems and particularly to signalsystems having dynamic regulators governed by pilot current.

One object of the invention is to provide a signal system havingregulators under control of pilot current that shall prevent exaggeratedtransient transmission irregularities,

Another object of the invention is to provide a signal transmission linehaving dynamic regulators under control of pilot current for governingthe strength of the transmitted signals that shall divide the line intosections in a manner to permit the free transmission of signal currentsfrom one section to another section and to control the pilot current ina section according to the integrated variations of the pilot current ina preceding section while preventing the transmission of transientexaggerated irregularities from one section to another section.

A further object of the invention is to provide a signal transmissionline of the above-indicated character that shall divide the line intosections by blocking the transmission of pilot current from one sectionto another section while permitting the free transmission of signalcurrents from one section to another section and that shall reintroduceconstant amplitude pilot current in a subsequent line section which iscontrolled according to the integrated variations of the pilot currentin the preceding line section.

In long signal transmission lines provided with dynamic regulatorsgoverned by pilot current for controlling the strength of the linesignals, trouble is at times experienced by reason of exaggeratedtransient transmission irregularities. If there is a change in thestrengths of the signal and pilot currents, the pilot current governsthe dynamic regulators to correct for the change in the strength of thesignals. A number of the regulators make correction for the change inthe signal strength with the result that an overcompensation is effectedfor the change in signal strength. Then during a period of time thepilot current operates the regulators to efiect an oscillatory movementof the signal strength'above and below normal value until a steadynormal state is reached. The longer the transmission line is in length,the greater will be the transient swings in the signal strength.

The present invention provides means for limiting the transienttransmission irregularities on a signal transmission line provided withdynamic regulators, The transmission line is divided into sections withblocking means to prevent the transmission of the transientirregularities from one section to another section while permitting thefree transmission of signal currents from one section to anothersection.

In one form of the invention a blocking filter is inserted in the signaltransmission line with dynamic regulators placed on each side of theblocking filter. The blocking filter permits the free transmission ofsignal currents therethrough while preventing the transmission of thepilot current which controls the 'dyamic regulators. A source ofconstant level pilot current is connected tov the line section beyondthe blocking filter. The pilot current from this source is controlled inaccordance with the integrated variations of the pilot current on theline section before the blocking filter. A resistance element having anegative temperature coefiicient of resistance is inserted in thecircuit between the source of pilot current and the line section beyondthe blocking filter. This resistance element is controlled by a heatercoil which, in turn, is governed by the pilot current on the linesection before the blocking filter.

A filter which selects the pilot frequency is connected to the linesection before the blocking filter. The output from the pilot filter isamplified and then rectified. The rectified current is amplified andsupplied to the heater coil for controlling the resistance element inthe pilot current circuit connected to the line section beyond theblockin filter. In the above manner the variations in the pilot currenton the line section before the blocking filter are integrated forcontrolling the pilot current impressed on the line section beyond theblocking filter. The transient transmission irregularities in the linesection before the blocking filter are not transmitted to the linesection beyond the blocking filter. However, the integrated value ofthe'pilot current variations on the line section before the filter isemployed to control the pilot current on the line section beyond thefilter.

In the accompanying drawing:

Fig. 1 is a diagrammatic View of a signal system constructed inaccordance with the invention; and

Fig. 2 is a modification of the signal system shown in Fig. 1.

Referring to Fig. 1 of the drawing, a transmission line comprisingconductors l and 2 is provided with a number of amplifiers four ofwhich, 3, 4, 5 and 6, are shown. The amplifiers 3, 4, 5 and 6 may be ofany suitable type and are controlled by regulators T, 8, 9 and Ill. Theregulators may be of the type disclosed in the patent to R, R. Blair2,179,915, November 14, 1939. The regulators are of the dynamic type andeifect a quick response in correcting any change in the signal strength.Carrier current signals are carried by the line comprising conductors Iand 2 and a pilot current supplied by a source II is provided forcontrolling the operation of the regulators.

A signal transmission line constructed as above indicated and providedwith dynamic regulators for controlling the amplifiers is liable to besubjected to exaggerated transient irregularities. If there is a changein the signal strength, the pilot curent will operate each of theregulators for correcting the signal currents. Inasmuch as a number ofregulators attempt to make the corrections, it is apparent thatovercompensation will be effected. The signal strength will be carriedabove and below normal value for a period of time. These transientirregularities will increase according to the length of the line and thenumber of amplifiers thereon.

In order to limit the transient irregularities which may be transmittedalong the conductors I and 2, the line is divided in sections by meansof a pilot blocking filter I2. The filter I2 blocks the transmission ofpilot current and permits the free transmission of the signal currents.A new pilot current which may have the same frequency as the source IIor a different frequency is supplied from a source I3 to the linesection beyond the blocking filter I2. The circuit be-. tween the sourceI3 and a line section beyond the filter I2 includes apilot filter I4 anda resistance element I5. The resistance element negative temperaturecoefficient. of resistanceand may, for example, be composed of silversulphide. The resistance element I5 is controlled by a heater coil I6 togovern the strength of the pilot current supplied from the source I3according to the integrated variations of the pilot current on the. linesection before the filter I2.

A control circuit I1 which is connected to the line. section before thefilter I2 is provided for controlling the heater coil IS. The circuit IIcomprises a pilot filter I8, an amplifier tube I9, a two-elementrectifier tube and a direct current amplifier tube 2!. The pilot filterI8 is directly connected to the line section before the filter I2. Theoutput circuit from the filter I8 is connected to the input. circuit ofthe amplifier I9. Plate potential for the amplifier tube I9 and also forthe amplifier tube 2I is supplied by a battery 22. The alternatingcurrent output. circuit of the tube I9 comprises a tuned circuit 23 anda condenser 24. The rectifier tube 29 is coupled to the output circuitof the tube I9 by means of a condenser 25 and a resistance element 26.The rectifier circuit of the tube 20 includes the resistance element 26and resistance .2

element 21. The potential drop across the resistance element 21 isimpressed on the grid of the direct current amplifier 2I. The outputcircuit of the direct current amplifier 2i includes a resistance element28, the potential drop across which is impressed on the heating coil I5.

In a signal system constructed as above indicated signal currents may befreely transmitted from one end of the line to the other whereas pilotcurrent from the source I I cannot be transmitted beyond the pilotblocking filter I2. Accordingly, any transient swings produced on theline section before the blocking filter I2 cannot be transmitted to. theline section beyond the I5 has a .n

blocking filter. It is necessary, however, to con reference characters.

trol the pilot current from the source I3 accord-' ing to the integratedvalue of the pilot current on the line before the blocking filter I2.Control of the pilot current from the source I3 according to theintegrated value of the pilot current before the blocking filter iseffected by means of the control circuit I'I. Although only one blockingfilter is shown in Fig. l of the drawing, it is to be understood thatany number of blocking filters may be employed to divide the line intoany desired number of sections.

The system shown in Fig. 2 of the drawing is a modification of thesystem shown in Fig. 1 and like parts have been indicated by similar Theline shown in Fig. 2 is divided into sections by a pilot blocking filterthe same as the line shown in Fig. 1. Moreover, a control circuit I!which is similar to the control circuit I'I shown in Fig. l is providedfor controlling a heater coil It. A circuit 38 comprising an overloadedamplifier tube BI and a pilot filter 32 is provided for supplying pilotcurrent to the line section beyond the blocking filter I2. The inputcircuit of the amplifier tube 3i is connected across the output circuitof the amplifier tube I9. The overloaded amplifier tube BI is thussupplied with amplified pilot current from the line section before theblocking filter I2. The output current from the amplifier tube 3| has asubstantially constant amplitude and is supplied through a transformer33, the pilot filter 32 and a resistance element 34 to the line sectionbeyond the blocking filter I2. The resistance element 34 has a negativetemperature coefficient of resistance and is similar to the resistanceelement I5 shown in Fig. 1 of the drawing. The resistance element 34 iscontrolled by control circuit I'I according to the integrated pilotvariations on the line section before the blocking filter I2.

Modifications in the systems and in the arrangement and location ofparts may be made within the spirit and scope of the invention and suchmodifications are intended to be covered by the appended claims.

What is claimed is:

1. In a signal system a signal transmission line, blocking means on theline dividing it into sections, means supplying pilot current to saidsections on each side of the blocking means, said blocking meanspreventing the transfer of pilot current therethrough while permittingthe free transfer of signals therethrough, amplifiers in respectivesections each including a regulator controlled by the pilot current inits section and attaining a state of stable operation within a limitedperiod of time after a change occurs in pilot current strength, andmeans for controlling the pilot current beyond said blocking meansaccording to the integrated variations of the pilot current before theblocking means integrated over a period of time greater than saidlimited period required for said regulator to attain a state of stableoperation.

2. In a signal system, a transmission line, blocking means dividing theline into sections, dynamic regulators on each side of said blockingmeans, means impressing pilot current on the line on each side of saidblocking means for controlling the dynamic regulators, said blockingmeans preventing the transfer of pilot current therethrough whilepermitting the free transfer of signals therethrough and said dynamicregulators attaining a state of stable operation Within a limited periodof time after a change occurs in said pilot current strength, and meansfor con trolling the pilot current beyond said blocking means accordingto the integrated variations of the pilot current before the blockingmeans integrated over a period of time greater than said limited periodrequired for said regulators to attain a state of stable operation.

3. In a signal system, a transmission linehaving a plurality of dynamicregulators thereon controlled according to the strength of pilotcurrent, said dynamic regulators attaining a state of stable operationwithin a limited period after a change occurs in the strength of saidpilot current, blocking means on said line for the pilot currentfrequency dividing the transmission line, means for reintroducing pilotcurrent in the line beyond said blocking means, and means forcontrolling said reintroduced pilot current according to the average ofthe fluctuations in the pilot current before said blocking meansaveraged over a period approximately equal to that required by saidregulators to attain a state of stable operation after the occurrence ofa change in the strength of the controlling pilot current.

4. In a signal system, a transmission line carrying signal currents andpilot current, blocking means on said line for the pilot currentfrequency, dynamic regulators for said line on each side of saidblocking means, means for impressing pilot current on the line beyondsaid blocking means, said dynamic regulators being controlled by thestrength of the pilot current in the respective portions of the line andattaining a state of stable operation Within a limited period after achange occurs in said pilot current strength, and means controlled bypilot current on the line before said blocking means for governing thepilot current introduced in the line beyond the blocking means inaccordance with the integrated value of the pilot current variationsbefore the blocking means integrated over a period approximately equalto that required by the regulators to attain a state of stable operationafter the occurrence of a change in the strength of the pilot current 5.In a signal system, a signal transmission line, a blocking filterdividing the line into sections, dynamic regulators on each side of saidfilter, means impressing pilot current on each side of said filter forcontrolling the dynamic regulators, said blocking means preventing thetransfer of pilot current therethrough while permitting the freetransfer of signals therethrough and said dynamic regulators attaining astate of stable operation within a limited period after a change occursin the strength of said pilot current strength, a circuit for supplyingpilot current to the line beyond said filter, resistance means in saidcircuit for governing the pilot current, and means for controlling saidresistance means according to integrated variations of the pilot currenton the line before said filter integrated over a period of timeapproximately equal to that required by the regulators to attain a stateof stable operation after the occurrence of a change in .the strength ofthe pilot current 6. In a signal system, a signal transmission linehaving signal currents and pilot current thereon, a blocking filter onsaid line permitting the free fiow of signal currents therethrough andblocking the passage of pilot current, dynamic regulators on each sideof said filter for controlling the signal currents, a source of pilotcurrent connected to the line beyond said filter, said dynamicregulators being controlled by the strength of the pilot current in therespective portions of the line and attaining a state of stableoperation within a limited period after a change occurs in the strengthof said pilot current, a resistance element having a negativetemperature coefilcient of resistance for governing the pilot currentfrom said source, and means controlled according to the integratedvariations of the pilot current on the line before said filterintegrated over a period of time approximately equal to that required bythe regulators to attain a state of stable operation after theoccurrence of a change in the strength of the pilot current forgoverning the temperature of said resistance element.

'7. In a signal system, a signal transmission line having signalcurrents and pilot current thereon, a blocking filter for dividing theline into sections, amplifiers including dynamic regulators on each sideof said filter, said filter blocking the flow of pilot current andpermitting the free flow of signal currents, a source of pilot currentconnected to the line beyond said filter, said dynamic regulators beingcontrolled by the strength of the pilot current in the respectiveportions of the line and attaining a state of stable operation within alimited period after a change occurs in the strength of said pilotcurrent, a resistance element having a negative temperature coeificientof resistance for governing the pilot current from said source, a heaterelement for controlling the temperature of said resistance element, apilot filter for obtaining pilot current from the line before saidblocking filter, and means for amplifying and rectifying said selectedpilot current to,

control said heater and govern the pilot current beyond said blockingfilter according to the integrated variations of the pilot current on.the line before the blocking filter integrated over a period of timeapproximately equal to that required by the regulators to attain a'stateof stable operation after the occurrence of a change in the strength ofthe controlling pilot current.

8. In a signal system, a signal transmission line having signal currentsand pilot current thereon, a blocking filter for dividing the line intosections, said filter blocking the fiow of pilot current and permittingthe free flow of signal currents therethrough, dynamic regulators on theline on each side of said blocking filter under control of pilotcurrent, a pilot filter connected to the line before said blockingfilter for selecting the pilot frequency, means for controlling aportion of the output from the pilot filter .to obtain a constant outputand for supplying this constant output pilot current to the line beyondthe blocking filter, and means controlled by the integrated output fromthe pilot filter for governing the pilot current supplied to the linebeyond the blocking filter.

9. In a signal system a signal transmission line having signal currentsand pilot current thereon, a blocking filter for dividing the line intosections, said filter blocking the fiow of pilot current and permittingthe free flow of signal currents therethrough, dynamic regulators on theline on each side of said blocking filter under control of pilotcurrent, a pilot filter connected to the line before said blockingfilter for selecting the pilot frequency current, control meanscomprising an overloaded amplifier operating on a portion of the pilotfilter output for obtaining a constant pilot current and for supplyingthe constant pilot current to the line beyond the blocking filter, aresistance element having a negative temperature coefiicient ofresistance inserted in the connection of the constant pilot current tothe line, a heater coil for controlling said resistance element, andmeans controlled by the integrated output from the pilot filter forcontrolling said heater coil to govern the pilot current supplied to theline beyond said blocking filter.

10. In a Signaling system a signal transmission line, means to impresspilot current on said line, a plurality of amplifiers included in saidline at separated points, dynamic regulators individual to saidamplifiers for controlling the gain of said amplifiers in accordancewith the strength of the pilot current at the said respectiveamplifiers, said regulators responding to changes in pilot currentintegrated over a limited period of time, and a slow-acting pilotregulator located at a point in said line between groups of saidamplifiers for controlling the strength of the pilot current transmittedto the group of amplifiers toward the receiving end of said line inaccordance with the strength of the pilot current incoming from thegroup of amplifiers toward the transmitting end of said line, saidsloweacting regulator responding only to changes in pilot currentintegrated over a longer period of time than that over which changes inpilot current are integrated to efiect response in said individualdynamic regulators. BORIS J. KINSBURG.

